Photon-photon collisions and photon "decay"

[maka89]

Hello.

I want to play around with the process of one photon splitting into more lower energy photons and vice versa.

As I understand it one can quite easily make a Feynman diagram of a photon splitting into two lower energy photons by interacting with virtual electron/positrons. And also the reverse diagram is possible.

Questions:
- Once after getting the Feynman amplitudes for the splitting process, can one use the golden rule for Decays in a straight forward manner as one could for weak decays?

- Which diagrams are more dominant? Is it sufficient to just use gamma -> gamma gamma, or is it necessary to for instance also include gamma -> gamma gamma gamma.

 

[mfb]

As I understand it one can quite easily make a Feynman diagram of a photon splitting into two lower energy photons by interacting with virtual electron/positrons. And also the reverse diagram is possible.

Yes, but it won't happen in vacuum, all the amplitudes add to zero.
I don't find the reference I was looking for, but here one that needs to introduce violations of Lorentz invariance for the process: arXiv:hep-ph/0212382

 

[maka89]

Okay, thanks =)
Are there any other similar processes that allow for this kind of phenomenon(photons splitting or merging). I saw a paper on gamma -> 3xgamma, but that was in a strong magnetic field. How about 2xgamma -> 3xgamma ?

 

[mfb]

That might work (but odd<->even tends to be tricky as far as I know).
2 photons -> 2 photons or 4 photons certainly works, but the cross-section is really tiny.

 

[Vanadium 50]

Odd -> even (and vice versa) will never work. (proven by Wendell Furry)

Momentum-energy conservation strongly constrains what processes are allowed.

 

[PAllen]

See this thread (in links at bottom of this thread):

https://www.physicsforums.com/threads/decay-of-photons.512811/

Which discussed the 'decay' part of this at length, turning up key historical references.

 

[jimgraber]

http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.111.080405
This reference (above) seems to seriously discuss the possible direct observation of the scattering part.

Jim Graber

 

[jimgraber]

One quote from the reference in my previous post:
"The whole process appears as two photons ricocheting off each other, but it has only been observed indirectly by its effect on the magnetic moments of the electron and muon."

 

[mfb]

but a new analysis in Physical Review Letters shows that the Large Hadron Collider (LHC) at CERN could detect around 20 photon-photon events per year.

I didn't see this analysis, but to separate 20 events per year from background you need an extremely clean signature. Like particles in the TeV-range, and I would be surprised if they expect their production.

 

[bcrowell]

The following may be helpful:

http://physicsforums.com/showthread.php?t=512811
http://arxiv.org/abs/hep-th/9508018
http://physics.stackexchange.com/questions/12488/radioactive-decay-of-massless-particles

 

[vanhees71]

As far as I know, Delbrück scattering has not been observed yet, but there's nothing in principle against it. To the contrary, since it's a QED process, I'd expect it to really exist and even the prediction of the cross section should be quantitatively correct.